Conventionally, so-called two-piece cans are manufactured by punching aluminum or steel metal sheets used for can manufacturing, drawing and ironing to form a bottomed cylindrical can body, and after filling the can body with beverage or food, an upper lid is mounted thereto and seamed to seal hermetically. Here, to prevent corrosion caused by the contact of the can and the beverage or food contained inside, usually, the inner face of the can is protected by coating or applying a resin to the surface of metal sheet. However, in metal sheets that are coated or applied with such resin, since a large force is applied to the metal surface being the inner face at drawing and ironing during formation of a two-piece can, resin coatings peel off, and the beverage or food may reach the metal surface from the peeled area and cause corrosion.
On the other hand, recently, from environmental considerations for resource savings, thinning of can bodies is strongly desired. Accordingly, to maintain sufficient intensity for thinned can body, annular uneven beads are provided onto can body parts. Moreover, in two-piece cans, since the upper lid is mounted onto the upper end face of the can body and seamed, the outer peripheral diameter of the upper lid will be larger than the outer peripheral diameter of the can body part or the bottom part, unless specific treatment such as neck-in processing is applied. Further, as cans cannot be arranged efficiently and neatly when cans have such deviations in their outer peripheral diameters, efficiency for manufacturing, transportation or selling will be poor. Therefore, so-called bottom rims are formed, which makes the outer peripheral diameter of the bottom face of the can the same as the outer peripheral diameter of the upper lid by pressing and extending the outer periphery of the bottom of the can outwards. However, when uneven beads or bottom rims are formed after drawing and ironing, since not only adhesion of the coating resins are lowered, but also the state of the surface coating will be damaged. Therefore, corrosion is likely occur. Further, when it is used for food cans which contain more salt, corrosion is likely to occur immediately when only a small amount of the resin layer peel off.
To these problems, for example, in Patent Literature 1, before and after performing the processes to the can body, by quenching after heating the resin-coated metal sheet to the melting point of the resin or higher, the resin becomes amorphous and adhesion of the metal sheet surface and the resin are enhanced to prevent peeling off of the resin layer, such that corrosion resistance and impact resistance are improved. However, the method disclosed in Patent Literature 1 is aimed at forming process of a two-piece bottle type cans for containing beverage, and it could not be said that is suitable for manufacturing a two-piece food cans having uneven beads and bottom rims.